Display method for display apparatus

ABSTRACT

A method of driving a display apparatus with which unevenness of image is precluded and the time for display is shortened. A display apparatus for displaying an image by impressing a voltage on pixels by row electrodes and column electrodes disposed in a matrix, for example, a metal deposition type electrochemical display apparatus. A voltage not less than a threshold voltage V th  is selectively impressed on predetermined pixels by superposing an address pulse voltage V adress-row  for the row electrodes and an address voltage V adress-col  for the column electrodes on each other to thereby perform address driving, and a data sustaining pulse voltage V sus  is impressed on the row electrodes immediately after the address pulse voltage V adress-row . The data sustaining pulse voltage V sus  satisfies the condition of the following formula:
 
V sus +V adress-col &lt;V th   (1).

This application is a 371 of PCT/JP03/06154 May 16, 2003.

This application claims priority to Japanese Patent Application NumberJP2002-144450, filed May 20, 2002 which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a driving method suitable forapplication to, for example, an electrodeposition type display apparatusfor displaying images by deposition and dissolution of a metal, andparticularly to a driving method for a simple matrix type displayapparatus for driving by row electrodes and column electrodes which arearranged in a matrix.

BACKGROUND ART

In recent years, attendant on the spread of networks, documents hithertodistribution in the form of printed matter have come to be transmittedin the form of electronic documents. Further, books and magazines havecome to be often provided in the form of the so-called electronicpublishing. In order to read these pieces of information, reading fromCRTs (cathode ray tubes) and liquid crystal displays of computers hasconventionally been widely conducted.

However, in a light emission type display such as the CRT, it has beenpointed out that the display causes conspicuous wearing on an ergonomicground and, therefore, is unsuited to long-time reading. In addition,even a light reception type display such as a liquid crystal display issaid to be similarly unsuited to reading, because of the flickeringwhich is intrinsic of fluorescent tubes. Furthermore, both of the typeshave the problem that the reading place is limited to the places wherecomputers are disposed.

In recent years, reflection type liquid crystal displays not using abacklight have put to practical use. However, the reflectance innon-display (display of white color) of the liquid crystal is 30 to 40%,which means a considerably bad visibility, as compared with thereflectance of printed matter printed on papers (the reflectance of OApapers and pocket books is 75%, and the reflectance of newspapers is52%). In addition, the glaring due to reflectors and the like are liableto cause wearing, which also is unsuited to long-time reading.

In order to solve these problems, the so-called paper-like displays andthe so-called electronic papers have been being developed. The mediamainly utilize coloration by moving colored particles between electrodesthrough electrophoresis or by rotating dichroic particles in an electricfield. In these methods, however, the gaps between the particles absorblight, with the result that contrast is worsened and that apractical-use writing speed (within one sec) cannot be obtained unlessthe driving voltage is 100 V or higher.

As compared with the displays of these systems, electrochemical displaydevices for color development based on an electrochemical action(electrochromic display: ECD) is better in contrast, and they havealready been put to practical use as light control glass or timepiecedisplays. It should be noted here that the light control glass andtimepiece displays are not directly suited to the electronic paper orthe like uses, since it is intrinsically unnecessary to perform matrixdriving. Besides, they are generally poor in quality of black color, andthe reflectance thereof remains at a low level.

In addition, in such displays as electronic papers, they are continuedlyexposed to solar light or room light on a use basis, and, in anelectrochemical display device put to practical use in the light controlglass and timepiece displays, an organic material is used for formingblack-colored portion, which leads to a problem concerning lightresistance. In general, organic materials are poor in light resistance,and the black color concentration thereof is lowered through fading whenused for a long time.

In order to solve these technical problems, there has been proposed anelectrochemical display device using metal ions as a material for colorchange. In the electrochemical display device, the metal ions arepreliminarily mixed into a polymer electrolyte layer, the metal isdeposited and dissolved by electrochemical redox reactions, and thechange in color attendant on this is utilized to perform display. Here,for example, when the polymer electrolyte layer contains a coloringmaterial, it is possible to enhance the contrast in the case where thecolor change occurs.

Meanwhile, in the metal deposition type electrochemical display devicebased on deposition and dissolution of the metal, a threshold voltagewhich is the deposition overvoltage is utilized to achieve display. Ineach pixel, the metal is deposited when a minus voltage in excess of thethreshold voltage is impressed between electrodes arranged in a matrixform, whereas the metal is dissolved when a plus voltage is impressedbetween the electrodes.

When it is tried to drive a display apparatus based on a simple matrixsystem by utilizing the threshold voltage, the degree of coloration ofthe pixel would vary according to the sequence of selection.

For example, where display as shown in FIG. 19 is conducted by use ofrow electrodes and column electrodes which are arranged in a matrix, theimpression of the voltage on the electrodes is performed following atime sequence as shown in FIG. 20A. Specifically, while a scan pulsevoltage is impressed sequentially on the row electrodes, a data pulsevoltage is impressed on the column electrodes only at the time ofcoloration. As a result, a voltage (scan pulse voltage+data pulsevoltage) in excess of the threshold voltage is impressed on selectedpixels to cause coloration (deposition of metal), and only the scanpulse voltage is impressed on non-selected pixels, so that metaldeposition does not occur in the non-selected pixels, and non-coloredstate is maintained there.

In this case, the driving is conducted on a line sequence basis, andthere has been confirmed a phenomenon in which the degree of colorationin the pixels arranged on a common column electrode becomes graduallydeeper according to the sequence of selection. This is due to thefollowing. In the pixel in which the coloration (deposition of silver)has once occurred, a tiny current flows and the coloration proceeds evenwhere a voltage below the threshold voltage is impressed. Therefore, asis clear from an example of current waveform in FIG. 20B, the scan pulsevoltage is impressed on the previously colored pixel, and a currentflows there, also at the time of coloration in the subsequent pixel. Forexample, in a pixel (R₁, C₃), after the selection period for writing byimpressing the scan pulse voltage at a row electrode R₁, the data pulsevoltage is impressed on a column electrode C₃ also during the selectionperiods of the row electrodes R₂ and R₃. Similarly, in a pixel (R₂, C₃),after the selection period for writing by impressing the scan pulsevoltage is impressed on the row electrode R₂, the data pulse voltage forthe column electrode C₃ is impressed during the selection period of therow electrode R₃. When the threshold voltage is once exceeded, theimpression of only these data pulse voltages causes a current to flowand causes the coloration (deposition of metal) to proceed.

Thus, the pixel selected in the beginning stage of image rewritingundergoes writing repeatedly, dependent on the data for the followingpixels. As a result, the substantial writing time is elongated accordingto the sequence of scanning, so that the writing concentration would beenhanced more than required.

In addition, in the conventional driving method as above, the metal suchas silver must be deposited stably at the time of coloration, so thatthe voltage must be impressed over a certain period. Where the silverdeposition characteristic of the panel is not uniform, the addressingtime must be conditioned to accord to the pixel which is the worst inthe characteristic. Therefore, the addressing period is elongated, andthe image rewriting time would be increased.

The present invention has been proposed for the purpose of solving theseproblems. Accordingly, it is an object of the present invention toprovide a method of driving a display apparatus with which it ispossible to moderate the non-evenness of pixels formed, and to shortenthe time for rewriting the image display.

DISCLOSURE OF INVENTION

In order to attain the above object, according to the present invention,there is provided a method of driving a display apparatus for displayingan image by impressing a voltage on pixels by row electrodes and columnelectrodes which are disposed in a matrix, wherein a voltage not lessthan a threshold voltage V_(th) is selectively impressed onpredetermined pixels by superposing an address pulse voltageV_(adress-row) for said row electrodes and an address voltageV_(adress-col) for said column electrodes on each other to therebyperform address driving, and a data sustaining pulse voltage V_(sus)satisfying the relationship of the following formula (1):V_(sus)+V_(adress-col)<V_(th)  (1)is impressed on the row electrodes immediately after the address pulsevoltage V_(adress-row).

For example, in a metal deposition type display apparatus, when avoltage of not less than the threshold voltage V_(th) is impressed onpixels by superposing the address pulse voltage V_(adress-row) for therow electrode and the address pulse voltage V_(adress-col) for thecolumn electrodes is impressed on pixels, deposition of the metalstarts, and nuclei of crystals are formed. When a data sustaining pulsevoltage V_(sus) is impressed subsequently to this, the deposition of themetal proceeds, and the amount of the metal (e.g., silver) deposited inthe colored pixels is controlled by the data sustaining pulse voltageV_(sus) independently from the address driving. The address drivingrequires only the formation of the nuclei of the metal, and it ispossible to reduce the address pulse voltage which would causenon-evenness of writing, and to shorten the selection period.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general plan view showing, partly in a broken state, oneexample of an electrodeposition type display apparatus.

FIG. 2 is a general sectional view showing one example of theelectrodeposition type display apparatus.

FIG. 3 is a general perspective view showing, partly in a broken state,a part of the electrodeposition type display apparatus.

FIG. 4 is a waveform diagram showing a triangular wave voltage impressedfor examining current-voltage transient response characteristic.

FIG. 5 is a characteristic diagram showing the current-voltage transientresponse characteristic in a metal deposition type electrochemicaldisplay apparatus.

FIG. 6 is a schematic diagram showing one example of monochromic displayusing 3×3 pixels.

FIGS. 7A and 7B are waveform diagrams showing one example of a drivingvoltage waveform in a driving method to which the present invention hasbeen applied.

FIGS. 8A and 8B are waveform diagrams showing one example of the drivingvoltage waveform in the case where a data sustaining pulse and a writingpulse are separated.

FIGS. 9A and 9B are schematic diagrams showing the manner of display inthe case where the driving method shown in FIGS. 8A and 8B is conducted.

FIG. 10 is a waveform diagram showing one example of the driving voltagewaveform in the case where the data sustaining pulse is continuouslyimpressed at a fixed interval.

FIG. 11 is a waveform diagram showing one example of the driving voltagewaveform in the case where the data sustaining pulse is continuouslyimpressed at a fixed interval.

FIG. 12 is a general plan view showing one example of 100 lines×100lines display apparatus.

FIGS. 13A and 13B are waveform diagrams showing the driving method inthe case where the display apparatus shown in FIG. 12 is driven by therelated art.

FIGS. 14A and 14B are waveform diagrams showing the driving method inthe case where the display apparatus shown in FIG. 12 is driven by thepresent invention.

FIG. 15A is a characteristic diagram showing current and voltage valuesagainst time, and FIG. 15B is a characteristic diagram showing theamount of accumulated electric charge and coloration density againsttime, in a pixel (R₁, C₁) in the case where the driving method accordingto the related art shown in FIG. 13 is adopted.

FIG. 16A is a characteristic diagram showing current and voltage valuesagainst time, and FIG. 16B is a characteristic diagram showing theamount of accumulated electric charge and coloration density againsttime, in a pixel (R₁₀₀, C₁₀₀) in the case where the driving methodaccording to the related art shown in FIG. 13 is adopted.

FIG. 17A is a characteristic diagram showing current and voltage valuesagainst time, and FIG. 17B is a characteristic diagram showing theamount of accumulated electric charge and coloration density againsttime, in a pixel (R₁, C₁) in the case where the driving method accordingto the present invention shown in FIGS. 14A and 14B is adopted.

FIG. 18A is a characteristic diagram showing current and voltage valuesagainst time, and FIG. 18B is a characteristic diagram showing theamount of accumulated electric charge and coloration density, in a pixel(R₁₀₀, C₁₀₀) in the case where the driving method according to thepresent invention shown in FIGS. 14A and 14B is adopted.

FIG. 19 is a schematic diagram showing one example of monochromicdisplay using 3×3 pixels.

FIGS. 20A and 20B are waveform diagrams showing one example of a drivingvoltage waveform in a conventional driving method, in which FIG. 20A isa waveform diagram showing a driving sequence, and FIG. 20B is awaveform diagram showing a voltage and a current (on row electrodebasis) impressed on pixels (R₁, C₃), (R₂, C₃), (R₃, C₃).

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the method of driving a display apparatus according to the presentinvention will be described in detail below referring to the drawings.

Prior to description of the driving method, an example of theconfiguration of a metal deposition type electrochemical displayapparatus suitable for application of the present invention will bedescribed.

The display apparatus in this example is an electrochemical displayapparatus for performing display by deposition and dissolution of ametal through utilizing electrodeposition characteristics and is drivenby a simple matrix driving method. Therefore, driving electrodes arecomposed of a first electrode group X₁, X₂, . . . and a second electrodegroup Y₁, Y₂, . . . orthogonal thereto, which are arranged to intersecteach other in a lattice form.

FIGS. 1 to 3 show a specific structure of the driving electrodes, inwhich stripe-form transparent column electrodes 2 corresponding to thefirst electrode group are formed on a transparent substrate 1. Inaddition, a base substrate 3 provided with stripe-form counterelectrodes (row electrodes) 4 corresponding to the second electrodegroup is disposed opposite to the transparent substrate 1, and thesubstrates are laminated with a polymer electrolyte layer 5therebetween. The transparent column electrodes 2 and the row electrodes4 are provided in predetermined numbers according to the number ofpixels, and their intersections constitute the pixels.

In the above configuration, for the transparent substrate 1, there canbe used transparent glass substrates such as a quartz glass plate, awhite sheet glass plate and the like, but they are not limitative.Examples of the material usable for the transparent substrate 1 includeesters such as polyethylene naphthalate and polyethylene terephthalate,polyamides, polycarbonate, cellulose esters such as cellulose acetate,fluoro-polymers such as polyvinylidene fluoride andtetrafluoroethylene-hexafluoropropylene compolymer, polyethers such aspolyoxymethylene, polyacetals, polystyrene, polyolefins such aspolyethylene, polypropylene and methylpentene polymer, and polyimidessuch as polyimide-amides and polyether imides. Where these syntheticresins are used as a support, they can be used as rigid substrates whichare not bent easily, and they can be used as film-form substrates havingflexibility.

As the transparent column electrode 2, there can be used, for example, amixture of In₂O₃ and SnO₂, i.e., so-called ITO film, and films coatedwith SnO₂- or In₂O₃. The ITO film and the SnO₂- or In₂O₃-coated film maybe doped with Sn or Sb, and MgO, ZnO and the like can also be used.

On the other hand, examples of a matrix (base material) polymer whichcan be used for the polymer electrolyte layer 5 include polyethyleneoxide, polyethyleneimine, and polyethylene sulfide having skeleton unitsrepresented by —(C—C—O)_(n)—, —(C—C—N)_(n)—, and —(C—C—S)_(n)—,respectively. These skeleton units serves as main chain structures,which may be provided with branches. In addition, polymethylmethacrylate, polvinylidene fluoride, polyvinylidene chloride,polycarbonate and the like are also preferable.

In forming the polymer electrolyte layer 5, a required plasticizer ispreferably added to the matrix polymer. Preferable examples of theplasticizer in the case where the matrix polymer is hydrophilic includewater, ethyl alcohol, isopropyl alcohol and mixtures thereof. On theother hand, preferable examples of the plasticizer in the case where thematrix polymer is hydrophobic include propylene carbonate, dimethylcarbonate, ethylene carbonate, y-buryrolactone, acetonitrile, sulfolan,dimethoxyethane, ethyl alcohol, isopropyl alcohol, dimethyl formamide,dimethyl sulfoxide, dimethyl acetamide, n-methylpyrrolidone and mixturesthereof.

The polymer electrolyte layer 5 is formed by dissolving an electrolytein the matrix polymer. Examples of the electrolyte include not onlymetallic salts functioning as a color forming material for display butalso quaternary ammonium halides (F, Cl, Br, I), alkali metal halides(LiCl, LiBr, LiI, NaCl, NaBr, NaI, etc.), alkali metal cyanides, andalkali metal thiocyanides, and a material containing at least onesupport electrolyte selected therefrom is dissolved as an electrolyte.Here, examples of the metallic ion constituting the metallic saltfunctioning as a color forming material for display include bismuth,copper, silver, lithium, iron, chromium, nickel, and cadmium, which maybe used singly or in combination. As the metallic salt, arbitrary saltsof these metals may be used. Where the metal is silver, the examples ofthe metallic salt include silver nitrate, silver borofluoride, silverhalides, silver perchlorate, silver cyanide, silver thiocyanide, etc.

Besides, a colorant may be added to the polymer electrolyte layer 5 inorder to enhance contrast. Where the coloration by deposition of themetal is black, the background color is preferably white, and a whitematerial high in hiding property is preferably used as the colorant. Assuch a material, white particles for coloring may be used; examples ofthe white particles for coloring include titanium dioxide, calciumcarbonate, silica, magnesium oxide and aluminum oxide.

In this case, the ratio in which the white pigment is mixes, in the caseof inorganic particles, is preferably about 1 to 20 wt. %, morepreferably about 1 to 10 wt. %, and further preferably about 5 to 10 wt.%. The reason for the restriction to within such a range of ratio isthat the white pigment such as titanium oxide is not soluble butdispersible in the polymer, and, when the mixing ratio is increased, thewhite pigment will coagulate, with the result that the optical densityis nonuniform. Besides, the white pigment lacks ionic conductivity, sothat an increase in the mixing ratio leads to a lowering of theconductivity of the polymer electrolyte. Considering both the abovepoints, the upper limit of the mixing ratio is about 20 wt. %.

Where the inorganic particles are mixed into the polymer electrolytelayer 5 as a colorant as above-mentioned, the thickness of the polymerelectrolyte layer 5 is preferably 10 to 200 μm, more preferably 10 to100 μm, and further preferably 10 to 50 μm. As the polymer electrolytelayer 5 is thinner, the resistance between electrodes is lower, whichpreferably leads to a shortening of coloration and decoloration timesand a reduction in electric power consumption. However, when thethickness of the polymer electrolyte layer 5 is less than 10 μm,mechanical strength is lowered, leading to such inconveniences asgeneration of pinholes or cracks. On the other hand, when the thicknessof the polymer electrolyte layer 5 is too small, the mixing amount ofthe inorganic particles is small, and the whiteness (optical density)may be insufficient.

Incidentally, where a coloring matter is used as the coloring materialmixed in the polymer electrolyte layer 5, the mixing ratio of thecoloring material may be 10 wt. % or below. This is because the coloringefficiency of the coloring matter is much higher than that of theinorganic particles. Therefore, an electrochemically stable coloringmatter can provide a sufficient contrast even when used in a smallamount. As such a coloring matter, for example, oil-soluble dyes arepreferably used.

The base substrate 3 provided on the back side may not necessarily betransparent, and any substrate, film or the like that can securely holdthe row electrodes 4 can be used. Examples of the usable materialinclude glass substrates such as quartz glass plates and while sheetglass plates, ceramic substrates, paper substrates, and wood substrates.Naturally, the usable material is not limited to these materials, andsynthetic resin substrates and the like can also be used. Examples ofthe material of the synthetic resin substrates include esters such aspolyethylene naphthalate and polyethylene terephthalate, polyamides,polycarbonates, cellulose esters such as cellulose acetate,fluoro-polymers such as polyvinylidene fluoride andtetrafluoroethylene-cohexafluoropropylene, polyethers such aspolyoxyethylene, polyacetal, polystyrne, polyolefins such aspolyethylene, polypropylene and methylpentene polymer, and polyimidessuch as polyimide-amides and polyether imides. Where these syntheticresins are used for the base substrate, they can be used as rigidsubstrates which it not bent easily, but they can also be used asfilm-form substrates having flexibility.

For the row electrodes 4, there can be used conductive materials, forexample, metallic materials. It should be noted here that where thepotential difference between the metal constituting the row electrodes 4and the metal to be deposited on the transparent column electrodes 2 islarge, electric charges are accumulated on the electrodes in the coloredstate, and the migration of the electric charges occur, which may resultin unintended coloring of pixels. Particularly, when the potentialdifference exceeds the deposition over-voltage at the time of deposition(threshold value in simple matrix driving), there is the possibility ofthe coloring. Therefore, for the row electrodes 4, it is desirable toselect a metal such that the potential difference between itself and themetal to be deposited as the coloring material is less than thedeposition over-voltage (threshold value). Ideally, as the metallicmaterial constituting the row electrodes 4, there is used a material inthe state before ionization of the metal ions used for the coloringmaterial (in the metallic state). Namely, the same metal as the metal tobe deposited and dissolved is used for the row electrodes 4, as, forexample, silver is used for the row electrodes 4 where the depositionand dissolution of silver are utilized. This ensures that theabove-mentioned potential difference will not occur in the conditionwhere the metal is deposited on the transparent column electrodes 2.

The configuration of the display apparatus utilizing theelectrodeposition characteristics is as above-described. Next, a methodof driving the display apparatus will be described.

In the display apparatus utilizing the electrodepositioncharacteristics, where a triangular wave voltage as shown in FIG. 4, forexample, is impressed between the column electrode and the rowelectrode, a current-voltage transient response characteristic shown inFIG. 5 is obtained. Incidentally, FIG. 5 shows an example ofcharacteristics in the case where the row electrodes are Ag electrodesand silver ions and iodide ions are dissolved in the polymerelectrolyte.

Referring to FIG. 5, as a voltage ranging from zero to the minus side isimpressed between the column electrode and the row electrode,non-deposition of silver is kept for a while, and deposition of silveronto the column electrode begins when the impressed voltage exceeds athreshold voltage V_(th). It is seen from FIG. 5 that a currentattendant on the deposition starts to flow when the voltage exceeds thethreshold voltage V_(th). Thus, each pixel has a characteristic suchthat a characteristic as a capacitor is mainly strong before deposition(white) and the resistance decreases as deposition proceeds (black).

The deposition of silver continues even when the impressed voltageexceeds a writing voltage V_(w) corresponding to the apex of thetriangular wave voltage and is gradually lowered, and the depositioncontinued even when the impressed is lowered below the threshold voltageV_(th). The deposition of silver ends when the impressed voltage islowered to a keeping voltage V_(ke). This implies an important finding.Specifically, it was found that when the impressed voltage once exceedsthe threshold voltage V_(th) and nuclei (seeds) are formed, thedeposition of silver occurs even at a voltage not higher than thethreshold voltage V_(th). The present invention makes most of thisphenomenon, as will be described later.

On the other hand, when a voltage of opposite polarity (plus) isimpressed between the column electrode and the row electrode,dissolution of silver begins, and the deposited silver disappears whenthe impressed voltage reaches an erasure voltage V_(ith). When a voltagehigher than this is impressed, iodine is librated to adhere to theelectrodes, whereby the electrodes are colored in yellow.

As for the driving of the display apparatus showing the current-voltagetransient response characteristic as above, it may be contemplated, mostsimply, to impress a voltage in excess of the threshold voltage inaddress driving so as to deposit silver and to write in the pixel, ashas been shown in FIG. 20B. However, as has been mentioned above, thereoccur the problems that the writing density becomes nonuniform and theaddressing period is elongated, leading to an increase in the pixelrewriting time.

In view of this, in this example, a data sustaining pulse is appliedimmediately after the data addressing period, whereby the amount ofsilver deposited on the colored pixels is controlled independently fromthe address pulse. Now, for simplifying the description, a monochromicdisplay by use of 3×3 pixels shown in FIG. 6 is taken as an example, andthe driving voltage waveform in this case will be described.

FIGS. 7A and 7B show an example of driving voltage waveform forperforming display according to the present invention, in the case of anelectrodeposition display device such that silver is deposited on thecolumn electrode when a minus voltage is impressed and the voltagebecomes greater than the threshold voltage V_(th) and that silver isdissolved when a plus voltage is impressed. In FIG. 7(B), there areshown a row voltage impressed on each of row electrodes R₁, R₂, R₃, acolumn voltage impressed on each of column electrodes C₁, C₂, C₃, and avoltage impressed on pixels (R₁, C₃), (R₂, C₃), (R₃, C₃).

At the time of display, an address pulse voltage V_(adress-row) at|V_(th)| is impressed on each of the row electrodes R₁, R₂, R₃, and asignal writing address pulse voltage V_(adress-col) (0 to V_(th))smaller than the threshold voltage V_(th) is impressed on each of thecolumn electrodes C₁, C₂, C₃, whereby the electrodes are selected in adownward order. In this case, a voltage (V_(adress-row)+V_(adress-col):2×|V_(th)| at maximum) greater than the threshold voltage V_(th) isimpressed only on the pixels for silver deposition, whereby silver isdeposited on the transparent column electrodes, and nuclei are formed.

For example, at the pixels (R₁, C₃), (R₂, C₃), (R₃, C₃), the addresspulse voltage of the column electrode C₃ and the address pulse voltageof the row electrodes R₁, R₂, R₃ are superposed on each other, resultingin that a voltage in excess of the threshold voltage is impressed due tothe voltage difference, and silver deposition takes place. On the otherhand, at the pixel (R₁, C₁) and the like, there is no period duringwhich the address pulse voltage of the column electrode and the addresspulse voltage of the row electrodes is superposed, and only a voltagebelow the threshold voltage V_(th) is impressed. Therefore, at thesepixels, silver deposition does not occur, and nuclei are not formed.

Here, it is unnecessary to complete the writing by the address driving,and it is necessary only to form crystals serving as nuclei, so that thedata addressing period for impressing the address pulse voltageV_(adress-row) and the address pulse voltage V_(adress-col) can be byfar shortened, as compared with the example shown in FIGS. 20A and 20B.Specifically, the data addressing period can be shortened to about 1/10times the writing time.

After the data addressing period, a data sustaining pulse voltageV_(sus) is impressed on the row electrodes R₁, R₂, R₃, . . . . With thedata sustaining pulse voltage V_(sus) impressed, it is possible tocontrol the amount of silver deposited and to uniformize the coloringdensity at each pixel. When the data sustaining pulse voltage V_(sus) isimpressed, the deposition is continued only at the pixels where thenuclei have been formed, whereby the deposition amount is controlled. Atthe pixels where the nuclei have not been formed, impression of the datasustaining pulse voltage V_(sus) does not cause deposition, andnon-colored state is maintained there. This is clear also from thedescription of FIG. 5.

The data sustaining pulse voltage V_(sus) is selected to be a voltagebetween the keeping voltage V_(ke) and the threshold voltage V_(th), andsatisfies the following conditional formula:V_(sus)+V_(adress-col)<V_(th)  (conditional formula 1)

When the data sustaining pulse voltage V_(sus) is increased beyond thisvalue, deposition of silver by the impression of the data sustainingpulse voltage V_(sus) takes place also at non-addressed pixels (pixelswhich must be kept in the non-colored state).

After the writing, the display can be memorized by opening orshortcircuiting both the column electrode and the row electrode. Inaddition, when an erasing voltage −V_(e) is impressed on the rowelectrodes R₁, R₂, R₃, . . . at a predetermined timing so as to impressa plus voltage V_(e) on each pixel, silver is dissolved, and erasure isperformed thereby. Incidentally, the erasing voltage V_(e) is set to beequal to or slighter lower than the erasing voltage V_(ith) in FIG. 5above. When the erasing voltage Ve exceeds the erasing voltage V_(ith),coloring may occur.

As has been described above, by use of the data sustaining pulse voltageV_(sus), the following effects can be obtained. First, the selectionbetween coloring and non-coloring of pixel depends only on the dataaddressing pulse, and the amount of silver deposited can be controlledby the data sustaining period (T_(sus)) for which the sustaining pulsevoltage is impressed, so that the data addressing period (T_(adress))can be shortened. The image rewriting time (T_(ref)) is determined bythe data addressing period (T_(adress)), the number N of row electrodes,and the data sustaining period (T_(sus)) as shown in the followingformula (2), so that shortening of the data addressing period(T_(adress)) is very effective. In the case of the above-mentioneddriving method, the data addressing period (T_(adress)) could be set tobe not more than 10 msec.T _(ref) =T _(adress) ×N+T _(sus)  (2)

Besides, also as to the problem of nonuniformity such that the pixelcoloring density increases according to the scanning order, theabove-mentioned driving method is effective. In the above drivingmethod, control of the silver deposition amount is conducted byimpressing the data sustaining pulse voltage, so that the voltage of theaddress pulse can be made comparatively low and the impressing time canbe shortened. Therefore, the amount of silver nuclei deposited by theaddress pulse is reduced, attended by a reduction in nonuniformity ofgrowth.

As an example of application of the above driving method, first, thedata sustaining pulse and the writing pulse can be separated from eachother, as shown in FIG. 8A (driving sequence) and FIG. 8B (voltageimpressed on the pixels (R₁, C₃), (R₂, C₃), (R₃, C₃) and current). Inthis case, at the addressing time, a certain degree of coloring proceedsat the selected pixels as shown in FIG. 9A, and the coloring iscompleted by impression of the writing pulse as shown in FIG. 9B. Therewriting time in this case is induced from the following formula:T _(ref) =T _(adress) ×N+T _(sus) +T _(write)  (3)where T_(write) is the writing time.

In addition, while the data sustaining pulse is impressed in successionto the addressing pulse in the above example, it is also possible, forexample, to continuously impress the data sustaining pulse with acertain interval, as shown in FIG. 10. Alternatively, it is alsopossible to intermittently impress the data sustaining pulse, as shownin FIG. 11. With these variations, it is possible to provide a degree offreedom in circuit designing.

Next, taking an actual panel operation as an example, the effects of thepresent invention will be described. Here, a panel having 100 lines ofrow electrodes and 100 lines of column electrodes as shown in FIG. 12 istaken as an example. In the case of the related art, for shortening thescreen rewriting time, a driving method as shown in FIG. 13A (voltagesimpressed on row electrodes and column electrodes) and FIG. 13B(voltages impressed on pixels and current waveform) is adopted. On theother hand, in the driving method according to the present invention, amethod as shown in FIG. 14A (voltages impressed on row electrodes andcolumn electrodes) and FIG. 14B (voltage impressed on pixels and currentwaveform) is adopted.

Here, first, the screen rewriting time in the case of the related art isone selection time (0.8 sec)×the number of lines (100)=80 sec, as isclear from FIGS. 13A and 13B, whereas the rewriting time according tothe present invention is one addressing period (0.02 sec)×the number oflines (100)+the data sustaining period (2 sec)=4 sec, as is seen fromFIGS. 14A and 14B. Therefore, as to the screen rewriting time, thedriving method of the present invention is by far advantageous.

In addition, as to the nonuniformity of coloring density, the amount ofelectric charges accumulated in each pixel was empirically determined,to give the results as shown in FIGS. 15A to 18B. Incidentally, FIG. 15Ashows the current and voltage values against time at pixel (R₁, C₁) inthe case where the driving method according to the related art shown inFIGS. 13A and 13B is adopted, and FIG. 15B shows the amount of electriccharges accumulated and the coloring density against time. FIG. 16Ashows the current and voltage values against time at pixel (R₁₀₀, C₁) inthe case where the driving method according to the related art shown inFIGS. 13A and 13B is adopted, and FIG. 16B shows the amount of electriccharges accumulated and the coloring density against time. FIG. 17Ashows the current and voltage values against time at pixel (R₁, C₁) inthe case where the driving method according to the present inventionshown in FIGS. 14A and 14B is adopted, and FIG. 17B shows the amount ofelectric charges accumulated and the coloring density against time. FIG.18A shows the current and voltage values against time at pixel (R₁₀₀,C₁) in the case where the driving method according to the presentinvention shown in FIGS. 14A and 14B is adopted, and FIG. 18 shows theamount of electric charges accumulated and the coloring density againsttime.

Based on the above, the difference in writing amount in the case whereall the pixels on the column line are colored will be discussed. First,from FIGS. 15A and 16B, in the driving method according to the relatedart, the amount of accumulated charges Q(R₁, C₁) at the pixel (R₁, C₁)and the amount of accumulated charges Q(R₁₀₀, C₁) at the pixel (R₁₀₀,C₁) are respectively Q(R₁, C₁)=221.8 mC/cm² and Q(R₁₀₀, C₁)=10.5 mC/cm²,so that the difference in the amount of accumulated charges is by afactor of about 21.

On the other hand, in the driving method according to the presentinvention, the amount of accumulated charges Q(R₁, C₁) at the pixel (R₁,C₁) and the amount of accumulated charges Q(R₁₀₀, C₁) at the pixel(R₁₀₀, C₁) are respectively Q(R₁, C₁)=11.9 mC/cm² and Q(R₁₀₀, C₁)=11.4mC/cm², so that the difference in the amount of accumulated charges isby a facto of about 1.04. Therefore, it is seen that, according to thepresent invention, the nonuniformity of density is improved remarkably.

INDUSTRIAL APPLICABILITY

As is clear from the above description, according to the presentinvention, it is possible to largely reduce the nonuniformity of imagesformed. In addition, since addressing can be performed at high speed, itis possible to shorten the time required for display.

1. A method of driving a display apparatus for displaying an image bydeposition and dissolution of a metal, the deposition and dissolutionbeing controlled at each pixel by impressing a voltage on the pixels byrow electrodes and column electrodes which are disposed in a matrix,wherein a voltage equal to or more than a threshold voltage Vth isselectively impressed on predetermined pixels by superposing an addresspulse voltage Vaddress-row, for said row electrodes and an addressvoltage Vaddress-col, for said column electrodes on each other in orderto cause deposition of the metal to begin, the voltage equal to or morethan the threshold being only momentarily applied to selected pixels toensure that deposition of the metal begins only at certain selectedpixels without exhausting an available amount of metal for depositionduring application of the voltage equal to or more than the threshold,and a data sustaining pulse voltage Vsus satisfying the relationship ofthe following formula (1):Vsus+Vaddress-col <Vth  (1) is thereafter impressed on said rowelectrodes immediately after said address pulse voltage Vaddress-row, inorder to cause additional deposition of the metal to continue.
 2. Themethod of driving a display apparatus as set forth in claim 1, whereinafter nuclei of crystal are formed in predetermined pixel by saidaddress driving, the amount of growth of said nuclei in the selectedpixels is controlled by the length of time said data sustaining pulsevoltage is imposed.
 3. The method of driving a display apparatus as setforth in claim 1, wherein said data sustaining pulse voltage isimpressed continuously during the sustaining period until the desiredamount of metal deposition occurs in the selected pixel.
 4. The methodof driving a display apparatus as set forth in claim 1, wherein saiddata sustaining pulse voltage is impressed intermittently during thesustaining period until the desired amount of metal deposition occurs inthe selected pixel.
 5. The method of driving a display apparatus as setforth in claim 1, wherein after said data sustaining pulse voltage isimpressed on a line sequence basis, a write pulse voltage is impressedon each row of the matrix.
 6. The method of driving a display apparatusas set forth in claim 1, wherein rewriting of the image is conducted inaddition to a series of operations for impressing an erasing pulsevoltage.
 7. The method of driving a display apparatus as set forth inclaim 1, wherein said data sustaining pulse voltage Vsus is a non-zerovalue.
 8. The method of driving a display apparatus as set forth inclaim 1, wherein the display apparatus includes a polymer electrolytelayer in which said metal is deposited, and said polymer electrolytelayer includes a pigment in the amount of 1-20% by weight, and is 10 to200 μm thick.
 9. The method of driving a display apparatus as set forthin claim 1, wherein the display apparatus includes a polymer electrolytelayer in which said metal is deposited, and said polymer electrolytelayer includes a pigment in the amount of 5-10% by weight, and is 10 to50 μm thick.
 10. The method of driving a display apparatus as set forthin claim 1, wherein the time it takes to write a new image to thedisplay is determined by the following formula (2):T _(ref) =T _(address) ×N+T _(sus)  (2) where T_(ref) is the total imagerewriting time, T_(address) is the data addressing period, N is thenumber of rows of electrodes in the matrix, and T_(sus)is the datasustaining period.
 11. The method of driving a display apparatus as setforth in claim 5, wherein the time it takes to write a new image to thedisplay is determined by the following formula (3):T _(ref) =T _(address) ×N+T _(sus) +T _(write)  (3) where T_(ref) is theis the total image rewriting time, T_(address) is the data addressingperiod, N is the number of rows of electrodes in the matrix, T_(sus) isthe data sustaining period, and T_(write) is the writing time.